1. Field of the Invention
This invention relates to fuel injection pumps.
2. Description of the Prior Art
The efficiencies of prior fuel injection pumps have been limited due to the tendency of such pumps to excessively aerate fuel and to insufficiently cool fuel before delivery to an associated injection nozzle. Since fule density is inversely related to the degree of aeration and fuel temperature, the weight of fuel delivered with each stroke of a constant volume pump is necessarily relatively low when fuel temperature is high or when the fuel is excessively aerated, with a corresponding decrease in pump efficiency. Uncontrollable aeration and fuel temperature result in uncontrollable fuel delivery rates and efficiency.
Fuel is supplied to prior fuel pumps through a single- or double-ported barrel communicating with either individual fuel lines or a manifold intermediate the pump and a fuel tank. A plunger received in the barrel has a recessed scroll surface on an end, or intermediate its ends, for receipt of fuel from at least one port. Fuel is expelled from the scroll to a nozzle during an injection stroke, with excess fuel being spilled to a return line through an outlet port.
Pump barrels having a single inlet/outlet port experience two-way flow through the port, causing heating and increased aeration of fuel. Previous double-port pump barrels fed directly from relatively high temperature fuel lines result in injected fuel of undesirably low density.
One type of injection fuel pump supplies fuel to a plunger bore through two axially staggered radial ports leading from an annular cavity about the pump barrel. Fuel is received through a port on the outer circumference of the barrel and is conveyed to a pumping chamber through an axial bore in the plunger. Supply and ejection of excess fuel requires two-way flow through the axial bore resulting in undesirable aeration. Further, spilled excess fuel is relatively hot and, when supplied to the pumping chamber, reduces the density of fuel available for injection.